An overlock sewing machine is provided with a plurality of loopers, and since it is necessary to thread each of the loopers with respectively different looper threads, threading operations were troublesome.
Patent Literature 1 discloses a device for threading a thread to a hollow looper point using compressed air.
In the above conventional device, when compressed air is sent to a thread path, a lever is manually pushed down for pushing a piston of an air pump in. Then, operations of the lever are directly linked with movements of the piston, so that the changes in lever operations have a direct effect on the movements of the piston. Namely, the velocities for pushing the piston differ with the forces for pushing down the lever. Accordingly, the flow velocities of compressed air were different depending on operations, so that there are some cases in which threads are not be delivered up to the looper points.